This invention relates to a transmission for vehicles of a kind which comprises:
a motion input shaft and at least two motion output shafts interconnected by a differential mechanism,
a storage reservoir for a differential mechanism lubricant,
a device for locking said differential mechanism,
a hydraulically operated actuator for selectively operating said locking device, and
a means of admitting a pressurized medium to said actuator.
A transmission with the above features is known, for example, from German Utility Model of DE-G 8911619.4.
In that transmission, the arrangement for operating the hydraulic differential lock actuator includes a piston pump which is driven by the rotational speed differential between the two crown wheels of the differential mechanism wherever a condition of the kind of a wheel spin occurs.
Accordingly, that structure only allows the differential to be locked after either wheel has entered a spinning condition. Thus, the differential can be locked neither ahead of a spin nor as both wheels of one axle are spinning at the same rate. In addition, with the differential locked, the actuator would be fed no more medium, and in the event of a leaky actuator, the differential locking action could soon become ineffectual.
On the other hand, there exist situations in the operation of a vehicle wherein the differential lock is expected to be operative with no difference in rotational speed between the wheels, such as preparatory to critical runs where even a temporary spin condition could defeat the vehicle capability to proceed or when the differential is locked to counteract the tendency of a vehicle to wander from a straight line travel path.
The transmission of the above-mentioned German Utility Model shows to be quite unsuited to such situations.
The pump linked operatively to the differential lock is, moreover, supplied with a medium stored in a separate reservoir from any storage reservoir for the differential lubricant.
It follows that, additionally to the need for a dedicated system branch-off for the delivery and return flows of the medium, usually an oil, to/from the actuator, any leakage therefrom may result in undesirably flooding the axle or at least the actuator case. It matters to observe that the working oil for the actuator is not always to the same specifications and composition as that intended for lubricating the differential, so that undesired problems may be caused by the two oils getting mixed together.
Further, also on this same account, the actuators require the provision of suitable seals and gaskets which, besides involving precision machining of the sealed surfaces, may become damaged or worn and result over time in the aforesaid leaky and flooded conditions.
The technical problem that underlies this invention is to provide a transmission whose construction and performance features can obviate the above-noted drawbacks with which the prior art is beset.